The present invention is directed to an improvement in the process disclosed and claimed in Klenk U.S. Pat. No. 4,113,773 (related to German application P 2,624,891). The entire disclosure of the Klenk patent is hereby incorporated by reference and relied upon.
It is known to produce benzoyl cyanide by the action of over stoichiometrical amounts of copper (I) cyanide on benzoyl chloride. The reaction is carried out at temperatures up to 80.degree. C. in acetonitril or benzonitrile or in ether with the addition of over stoichiometrical amounts of lithium chloride or lithium iodide (Normant et al, Bull. Soc. Chim. France (1972) pages 2402-2403) or at temperatures of 220.degree. to 230.degree. C. in the absence of a solvent (Org. Synth. Coll. 3, 112-114). At best these processes give a yield of 65%.
It is also known to convert benzoyl chloride to benzoyl cyanide by means of an alkali cyanide in a two phase system consisting of water and a solvent which is immiscible with water in the presence of a quaternary alkyl ammonium salt (Tetrahedron Letters No. 26 (1974), pages 2275 to 2278). In this process the yield only amounts to 60%.
Furthermore, it is known to produce benzoyl cyanide from benzoyl chloride by reacting water free hydrogen cyanide and an at least equimolar amount of pyridine (Z. Phys. Chem. 192 (1943), 200-201). This process gives yields of 78%.
A disadvantage of the known process is that there are formed by-products to a considerable extent, particularly the dimer of benzoyl cyanide (the benzoyloxyphenyl malodinitrile). Consequently, not only the yield of benzoyl cyanide is unsatisfactory but also its purity. Benzoyl cyanide can be separated from its dimer only with considerable difficulty and even then only incompletely.
Finally, it is known to carry out the reaction of benzoyl chloride to benzoyl cyanide in the presence of catalytic amounts of heavy metal cyanides by means of stoichiometric amounts of alkali metal cyanide at temperatures of 100.degree. to 300.degree. C. (German OS 2,614,242). The disadvantage of this process is that the benzoyl chloride is not completely reacted and the benzoyl cyanide recovered is contaminated by benzoyl chloride.
In Klenk U.S. Pat. No. 4,113,773 it is stated that the reaction according to the invention is carried out at temperatures of about 50.degree. to 160.degree. C., preferably at temperatures of 90.degree. to 130.degree. C. Although the pressure can be selected essentially at random (i.e., it is not critical) in order to use a simple apparatus it is advantageous to use a pressure which does not vary substantially from normal pressure, e.g., to use atmospheric pressure. In many cases because of the presence of volatile substances it can be suitable to use an elevated pressure corresponding to the temperature.
In several cases, it can be advantageous to add an inert solvent as a diluent. As such, inert solvents there can be used for example hydrocarbons, e.g., aromatic hydrocarbons such as benzene, toluene or xylene as well as mesitylene, ethyl benzene, cumene, p-cymene, t-butyl benzene or 1,3,5-triethyl benzene or aliphatic hydrocarbons such as ligroin with a boiling range of about 90.degree. to 140.degree. C., octane or decane or cyclic hydrocarbons such as decalin, cyclohexane and tetralin or halogenated hydrocarbons, particularly chlorinated aromatic or aliphatic hydrocarbons such as chlorobenzene, symmetrical tetrachloroethane, carbon tetrachloride, trichloroethylene, trimethylene bromide, ethylene dibromide. Also as the solvent there can be used for example ethers, e.g., dioxane, dibutyl ether, dioxolane, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol dimethyl ether or esters, e.g., alkyl esters such as butyl acetate, propyl acetate, amyl acetate, isobutyl acetate, octyl acetate, ethyl propionate, methyl butyrate, ethyl butyrate or methyl valerate. When an inert solvent is employed, the amount is not critical but it can be used for example in an amount of 10 to 5000 ml per mole of benzoyl chloride.
According to the invention the reaction takes place with alkali cyanides. Preferably there is used sodium cyanide or potassium cyanide. There also can be used lithium cyanide. Generally, it is suitable to employ at least a stoichiometric amount of cyanide. Advantageously, there is used about 1.05 to 3.0 equivalents of cyanide, especially 1.05 to 1.5 equivalents of cyanide, per mole of benzoyl chloride.
The reaction takes place in the presence of carboxylic acid nitriles. There can be used nitriles which are liquid under the reaction conditions and which are not changed. Especially suited are saturated aliphatic monocarboxylic acid nitriles of saturated aliphatic monocarboxylic acids with 2 to 6 carbon atoms, e.g., alkyl nitriles especially acetonitrile and isobutyronitrile. Other suitable nitriles include propionitrile, butyronitrile, valeronitrile, capronitrile or lauronitrile or unsubstituted aryl nitriles such as benzonitrile, o-toluo-nitrile, p-toluonitrile or m-toluonitrile.
The reaction furthermore takes place in the presence of copper (I) salts. There can be used both simple and complex copper (I) salts, particularly for example copper (I) cyanide, copper (I) chloride, copper (I) bromide and potassium tetracyanocuprate (I). There can also be used copper (I) fluoride, copper (I) iodide, copper (I) sulfate, copper (I) thiocyanate and sodium tetracyanocuprate (I).
The amount of nitrile and copper (I) salt to use depends in a given case on the type of nitrile and copper (I) salt and the reaction conditions, such as temperature and pressure, and in a given case on the type and amount of the solvent used as a diluent.
Generally, it is suitable to add at least 0.05 mole of nitrile per mole of benzoyl chloride. Although the nitrile can be used in a many times molar excess, it is advantageous to use not more than about 2 moles of nitrile per mole of benzoyl chloride. Preferably there is employed 0.1 to 1.0 mole of nitrile, especially 0.1 to 0.5 mole of nitrile.
It is generally suitable to use about 0.05 to 1.0 equivalent of copper (I) salt per mole of benzoyl chloride. Preferably there is employed 0.05 to 0.5 equivalent of copper (I) salt per mole of benzoyl chloride.
The cyanide is added as alkali cyanide. If the copper (I) salt used is a cyanide there can be eliminated entirely or partially an equivalent amount of alkali cyanide. However, it is generally advantageous to include not more than about 0.5 equivalent of cyanide in the form of copper salts.